PSLE 2012 - Science

[WOWee_]

RVHS:

thesjarox:

[quote=\"vaidyanathan padmini\"]How about friction question from McQ.....

My dd's answer is only C as friction opposes motion...
Only the box in c is moving so it should have friction

Confirmed with teacher-A,B and C.
Friction also acts on stationary objects. That's why forces have to overcome the friction before being able to move the object. Also, if there were no friction acting on an object,the object would glide across the surface, like ice, and would never stop.
Thus, A is also correct.

The force of friction is always exerted in a direction that opposes movement or potential movement between the two surfaces,
For B: Potential movement
For Movement
For A: non
So answer should be: B &C[/quote]
My answer for this question is (4) A, B & C. I thought about the surfaces in contact since if there was no friction the wooden block would be sliding around instead of remaining stationary.

[TF2010]

RVHS:

thesjarox:

[quote=\"vaidyanathan padmini\"]How about friction question from McQ.....

My dd's answer is only C as friction opposes motion...
Only the box in c is moving so it should have friction

Confirmed with teacher-A,B and C.
Friction also acts on stationary objects. That's why forces have to overcome the friction before being able to move the object. Also, if there were no friction acting on an object,the object would glide across the surface, like ice, and would never stop.
Thus, A is also correct.

The force of friction is always exerted in a direction that opposes movement or potential movement between the two surfaces,
For B: Potential movement
For Movement
For A: non
So answer should be: B &C[/quote]
I checked yahoo answers. Friction can act on stationary objects. The inertia of the mass at rest and the coefficient of friction between the two surfaces must be overcome.

[WOWee_]

fantasy1:

HI


How abt section (B) qn
Something abt the type of colour used for photosynthesis. For Part (C) when they removed the water plants, what observation will the person see to ensure result at part (B) is correct?

I'm not sure, but my answer was that he would observe about an equal number of fishes in each section when the water plants had been removed.

[RVHS]

The force of friction is always exerted in a direction that opposes movement or potential movement between the two surfaces,

For B: Potential movement
For Movement
For A: non
So answer should be: B &C[/quote]


I checked yahoo answers. Friction can act on stationary objects. The inertia of the mass at rest and the coefficient of friction between the two surfaces must be overcome.[/quote]

Aslo for Yahoo answer
the frivction exists everwhere between surfaces
but if there is no other force in the horizontal direction and it rests on the horizontal surface then there is no frictional force acting on itsometimes you push a heavy object but cant move it, here although it is stationary the force which resists motion is the frictional force hence it exists and has a value exactly equal to the force you have applied on it. but the frictional force can only reach a maximum value of coeffcient of friction * normal reaction
so once your applied force exceeds this value then it will have to start moving

[AIM]

Oh I think it is the metal spoon and the wet cloth wrapped around

[AIM]

I put swollen stem and broad leaves

[shengp]

kiasu学生:

What is the answer for the friction question in booklet A?

Hi ximinful,the ans is 4

[/quote]

what is the question? please helpppp! :lightrod:

[shengp]

Active kid:

777:

Can't remember. Only know that i put option 2. Wat is option 4 ?

I also put (4) --The air in the balloon had lost heat to the material of the balloon.

i put 3 i think... :whut:

[shengp]

found the paper manageble. section A: okay, but tricky :imcool:

Section B: damn hard sia! :gloomy:

[creamyhorror]

RVHS:

Aslo for Yahoo answer
the frivction exists everwhere between surfaces
but if there is no other force in the horizontal direction and it rests on the horizontal surface then there is no frictional force acting on it

I haven't seen the question, but I'll just lay out some enrichment material (for the people who are interested in physics):

If there's an object sitting on a flat platform, and the flat platform and object are moving sideways at a constant velocity together, then I would say there isn't any horizontal frictional force acting on the object.

However, if the platform is speeding up (accelerating), then there is definitely a frictional force acting on the object. That force is what causes the object to speed up along with the platform. Without that force, the object would slip backwards (due to its inertia).

It's like sitting on top of a car: if the car is cruising at a constant speed, you can sit easily. There's no friction pushing you sideways. If the car starts to speed up, friction between your bottom and the car surface is holding you there and pushing you forward, so that you can speed up along with the car. If the frictional force is insufficient, you'll slide backwards because your body isn't keeping up with the car, and possibly fall right off.